1. Field of the Invention
The present invention relates to a triode-type field emission device and method of manufacturing the same, and in particular to triode type field emission device having planar light source made by means of a screen printing process.
2. The Prior Arts
Following Cathode Ray Tube (CRT) Display and Liquid Crystal Display (LCD), Field Emission Display (FED) emerges as the most promising display technology of the next generation having great potential for future development. Compared with the displayer of the prior art, the Field Emission Display (FED) has the benefit of good displaying effect, wide vision angle, low power consumption, and compact size. In particular, in recent years, the field emission display of carbon nanotube, namely carbon nanotube field emission display (CNT-FED) is getting more and more attention.
In general, the structure of field emission display can be classified into a two-electrode structure and a three-electrode structure. The two-electrode structure is a field emission structure having an anode and a cathode, and its drawback is that, in application, it requires applying high voltage, thus its electron emission and uniformity are difficult to control. The three-electrode structure is an improvement of the two-electrode structure, a gate is added to control precisely the emission of electrons, thus having the advantages of requiring low voltage and small current to operate, and achieving self-emitting high illumination features of CRT. Therefore, in recent years, the three-electrode structure is very popular and has a good competitive edge in the market.
Wherein, the basic structure of the three-electrode structure is composed of a fluorescent layer of anode, an emission layer of cathode, and a gate. As shown in FIG. 1, the field emission device includes a cathode substrate 10 and an anode substrate 12 disposed parallel to each other, and a spacer column 14 is disposed in between as support to provide a vacuum space. The anode substrate 12 includes an anode layer 16 and a fluorescent layer 18; and the cathode substrate 10 includes a cathode layer 20, a gate layer 22, and a dielectric layer 24 in between. On the cathode layer 20 is produced a carbon nanotube to serve as an emission layer 26, the a hole 28 corresponding to the emission layer 26 is produced on the dielectric layer 24 and the gate layer 22 by means of lithographic process, hereby forming a point light source. In application, different voltages are applied on the anode layer 16, the cathode layer 20, and the gate layer 22. The gate layer 22 allows the electrons of the cathode layer 20 to be emitted from the emission layer 26, that passes through the hole 28 and impact on the fluorescent layer 18 of the anode substrate 12 through the acceleration of an electric field, in agitating the fluorescent layer 18 to emit lights.
Though the structure mentioned above is able to control effectively the direction of electron beams, yet the emission surface of the emission layer 26 is far lower than the gate layer 22, so that not only the threshold voltage of field emission is increased, the emission current density is decreased, but the electrons emitted are also liable to have greater angle of deflection due to the electric field of the gate layers 22 on two sides, thus making electrons impact on areas outside the fluorescent layer 18, in creating the problem of non-uniform light emission for images having central part dimmer and edge portion brighter. In addition, in case screen printing is used to produce carbon nanotube emission layer on the cathode layer 20, the electron emission thus produced is without a fixed direction, therefore, requiring further activation. The approach frequently utilized to solve the problem is to use a gum tape to pull up the flat carbon nanotube to be perpendicular to the cathode layer 20, however, this approach will make chemical material in the gum tape remain in the cathode layer 20 to create secondary pollution; besides, direct contact could destroy the structure and affect the stability and service life of the emission layer.
Therefore, presently, the design and performance of the field emission device is not quite satisfactory, and it has much room for improvements.